Biology subjects

Extavour, C. G.

Publications and source records attributed to Extavour, C. G..

At least 19 recordsLinked to original sources

bioRxiv2026

The Hox code abolishes anatomical variation in an insect gonad

Phenotypic traits can vary based on genes or environment. Nevertheless, some quantitative traits remain invariant. Understanding the developmental mechanisms that generate such invariance can reveal how phenotypic robustness evolves. Insect reproductive capacity is largely determined by the number of gamete-producing subunits within the gonad, providing a tractable system to investigate these mechanisms as they operate on a quantitative trait that impacts fitness. In most insects, gonad subunit number varies within and between species. Here, we investigate gonad development in the milkweed bug Oncopeltus fasciatus, wherein subunit number is invariant. We show that subunit number is established during embryogenesis, when some abdominal segments, but not others, specify somatic gonad precursors. The position and number of these precursors depend on segment identity, and experimentally modified segment number or Hox-mediated segment identity changes the number of gonad subunits. Thus, O. fasciatus establishes invariant subunit number by coupling gonad development to segmental patterning machinery. We propose that co-option of the Hox code provides a developmental mechanism for generating robustness in gonad subunit number and may thereby contribute to the evolution of reproductive capacity in other insects.

developmental biology↗

bioRxiv2026

A nuclear targeting approach enables efficient transgenesis in the milkweed bug Oncopeltus fasciatus

Insects show extreme diversity and have long intrigued biologists. Recent technological advancements, such as gene editing and transgenesis, should in principle enable the use of almost any insect species for biological research. However, in practice, species-specific challenges remain and conditions must be optimized carefully. Here, using the milkweed bug Oncopeltus fasciatus, we first generate a useful eye- and body-color mutant strain by using CRISPR/Cas9-mediated genome editing. Then we use this strain to develop an efficient piggyBac-mediated transgenesis system using a nuclear targeting approach. We show that incorporating 1x and 3x nuclear localization signals (NLS) into piggyBac mRNA substantially enhances overall transformation efficiency in O. fasciatus. Taking advantage of both the useful mutant strain and the efficient transgenesis system, we successfully integrated multiple expression cassettes ranging from 1.8 to 7.2 kb, including attP strains for phiC31-mediated site-specific integration and histone-labelled strains for live fluorescence imaging. We further provide evidence that the Q system, a binary expression system, is functional in this species, paving the way for future sophisticated genetic manipulations including functional assays for cis-regulatory elements. Together, our results not only expand the genetic toolkit of O. fasciatus as a comparative model insect, but also provide a practical framework for developing efficient transgenesis in other non-traditional model organisms.

developmental biology↗

bioRxiv2026

Repetitive sequence material shapes the earliest stages of de novo gene evolution in insects

A fundamental unresolved question in molecular evolution is how novel genes arise from noncoding DNA and become fixed within stable gene repertoires. Here, we performed comparative genomic analyses across evolutionary timescales in insects using chromosome-scale genome assemblies of two cricket species, Teleogryllus occipitalis and Tarbinskiellus portentosus. Using conservative criteria, we identified 41 de novo gene candidates derived from intergenic regions in the Te. occipitalis lineage. These genes are simple and compact, exhibit hallmarks of evolutionarily young genes, and frequently contain fragments of transposable elements and simple sequence repeats. Across insects, such repetitive sequence fragments show positional homology but lack sequence conservation in older genes, suggesting that they serve as sequence material for gene emergence during early stages of gene evolution. In contrast, insertions after gene establishment are strongly constrained. We propose a model in which stages of gene evolution are characterized by shifts in selective pressure on the incorporation of sequence material.

evolutionary biology↗

bioRxiv2026

Husbandry and Maintenance of Carausius morosus Laboratory Populations

Carausius morosus, the Indian stick insect, is a slender twig-like insect endemic to India. Though widely introduced through captivity around the world and commonly used in laboratories or kept as a household pet, standardized animal husbandry laboratory protocols are lacking. Here we report detailed laboratory culture conditions for C. morosus. We maintain stocks at 23 {degrees}C, 70% relative humidity, and a 12:12 hour light-dark photoperiod. This culture has been successfully sustained under these conditions for over two years, with standardized protocols in place for dietary and cage setup conditions. We also report methods for egg and hatchling care to support ongoing experiments with C. morosus. These standardized methods improve reproducibility and accessibility, enabling the broader use of C. morosus as a laboratory model system for developmental, behavioral, and physiological studies. SummaryThis paper outlines detailed protocols for maintaining a Carausius morosus laboratory colony, including key procedures for animal husbandry, egg and hatchling care, and an overview of the species lifespan and biological characteristics.

developmental biology↗

bioRxiv2026

Laboratory and wild Drosophila sechellia have conserved niche specialization phenotypes

A major challenge to investigating the proximate causes of ecological adaptation is the difficulty of studying the phenotypes of organisms in their natural environments. By necessity, many studies seeking to determine the genetic and cellular basis of adaptation therefore investigate potentially adaptive phenotypes under laboratory conditions where organisms are more easily experimentally manipulated. For laboratory models, it remains unclear if organisms maintained long term under laboratory conditions are representative of relatives in their natural environment. In recent years, Drosophila sechellia, a specialist species endemic to the Seychelles, has emerged as a (neuro)genetic model for studying the molecular basis of ecological adaptation. A multitude of studies have investigated the genetic and cellular basis of various aspects of this species specialization in a laboratory setting. However, the vast majority of these studies use laboratory strains of D. sechellia that were collected many decades ago, and have been maintained under conditions very different from their natural niche. Thus, it remains unclear if and how these strains resemble their wild counterparts. Here, we compare the phenotypes of these laboratory strains with recently-collected wild D. sechellia to ask if laboratory strains display a loss or degradation of phenotypes potentially involved in their specialization resulting from their long-term laboratory maintenance. Across several behavioral and anatomical phenotypes, we find a high degree of similarity between wild-caught and laboratory-maintained strains. Our results suggest that studies of the molecular mechanisms underlying D. sechellias phenotypes associated with specialization are likely representative of the evolution of these flies in the wild.

evolutionary biology↗

bioRxiv2025

Chromosome-scale genome assembly and annotation of the two-spotted cricket Gryllus bimaculatus (Orthoptera: Gryllidae)

The two-spotted cricket, Gryllus bimaculatus, is a key hemimetabolous model organism for developmental biology, neuroscience, and regeneration. The existing reference genome is, however, highly fragmented into 47,877 scaffolds, hampering chromosome-scale analyses for these fields. Here, we report a high-quality, chromosome-scale genome assembly for the white-eyed mutant strain of this cricket, generated using a combination of Nanopore and PacBio HiFi long reads, integrated with Hi-C data. The final 1.62 Gbp assembly achieves a scaffold N50 of 107.4 Mbp, a significant improvement in contiguity over the previous 6.3 Mbp N50. We anchored 94.45% of the assembly into 15 pseudomolecules, consistent with the known karyotype (n = 15). The genome completeness (BUSCO v6.0.0 insecta_odb12) reached 98.1%. We also updated the annotation, identifying 14,964 protein-coding genes. This gene set shows markedly improved completeness (BUSCO v6.0.0 insecta_odb12: 95.7%) compared with the previous annotation (81.2%) and successfully recovers all nine essential neuropeptide genes previously reported as missing from the draft assembly. This chromosome-scale genomic resource provides an essential foundation for comparative and functional genomics in G. bimaculatus.

genomics↗

bioRxiv2025

Lineage domains and cytoskeletal cables organize a cellular square grid in a crustacean

To build tissues, and ultimately functional bodies, cells in early embryos must arrange into specific patterns. In most animals, epithelial tissues exhibit a predominantly hexagonal space-packing geometry. However, in many species of the largest group of crustaceans, the Malacostraca, the embryonic epithelium takes on the striking form of a grid made up of predominantly square cells, sequential rows of which establish the adult segmented body plan. After square cells emerge, their organization appears to be maintained by specific cell division patterns. However, the mechanisms that initially generate square cells from hexagonal precursors are unknown. Here we address this problem by combining long-term multiview lightsheet microscopy, immunohistochemistry, laser ablation, and pharmacological perturbation. We show that in the emerging model crustacean Parhyale hawaiensis this highly unusual grid geometry is first initiated from two perpendicular axes that are established sequentially according to different cellular mechanisms. The first axis arises dorso-ventrally at a tensile lineage compartment boundary, while the second emerges at the anterior-posterior axis along the ventral midline through lineage-independent cell intercalation driven by tensile actomyosin cables. We show that these midline cables are necessary for organizing square-cell packing as well as for proper expression of the segmentation gene engrailed. Our findings show that both cell lineage-specific behaviors, as well as lineage-independent supracellular structures, are required to establish square grid epithelial organization and a segmented body plan.

developmental biology↗

bioRxiv2025

Heterotypic intercellular adhesion tunes efficiency of cell-on-cell migration

Cell migration across epithelial barriers occurs in diverse developmental, immunological, and pathological contexts. Here we investigate the contribution of heterotypic adhesion between migrating cells and epithelial "substrate" cells to transepithelial migration. Using an in silico model inspired by the migration of primordial germ cells across the midgut epithelium in the Drosophila embryo, we show that heterotypic adhesion modulates migration efficiency in a non-monotonic manner, revealing the existence of an optimal adhesion regime. Consistent with this prediction, in vivo overexpression of E-cadherin in germ cells accelerated their exit from the midgut relative to controls. Beyond providing experimentally testable predictions, our model integrates and explains previous observations on the role of heterotypic adhesion in cell-on-cell migration, offering a framework for understanding transepithelial migration across biological contexts. Significance StatementCell adhesion is important for cell migration, and when cells migrate on a substrate of other cells (rather than on extracellular matrix), the adhesive properties of both cell types must be considered. However, whether and how dynamic changes in adhesion regulate cell-on-cell migration remains unclear. Here we approach this problem using transepithelial migration of Drosophila embryonic germ cells as a case study. We develop an in silico model of the migration process that predicts an optimal level of adhesion between migrating cell and substrate cell to achieve efficient migration. In vivo live imaging and genetic manipulation experiments uphold the predictions of this model. This suggests that adhesion is not a simple on/off binary parameter regulating migration.

biophysics↗

bioRxiv2025

Evolutionary innovation through fusion of sequences from across the tree of life

Novel genes arise through multiple mechanisms, including gene duplication, gene fusion and horizontal gene transfer (HGT). While HGT has increasingly been documented in animals, the post-transfer evolutionary fate of horizontally-acquired genes is less well understood. We hypothesized that fusion with endogenous sequences in animal genomes might generate what we call "HGT-chimeras": genes with regions of non-metazoan and metazoan descent in the same open reading frame. To test this hypothesis, we developed a molecular phylogenetics pipeline that enables the identification of HGT-chimeras. We applied our pipeline to 319 high-quality annotated arthropod genomes and uncovered a high-confidence set of 274 HGT-chimeras corresponding to 104 independent origination events across diverse arthropods. HGT-chimeras contain intervals acquired from across the tree of life, and many likely originated via a gene duplication-based mechanism. To assess whether HGT-chimeras might be functionally important, we performed RT-PCR and Sanger sequencing of tissues from 20 arthropod species predicted to harbor HGT-chimeras in their genome. We found evidence for the expression of contiguous chimeric mRNAs for 36 of 41 tested HGT-chimeras across 18 of 20 different tested species. We also found evidence that HGT chimeras evolve under purifying selection and have acquired potentially functional domain architectures, consistent with the hypothesis that these genes are in active use and may participate in diverse biological processes. These results illuminate an underappreciated combinatorial mechanism underlying the origin of novel genes across the largest animal phylum, and suggest that interdomain sequence fusion can play important roles in animal biology and evolution. SignificanceEvolution forges novelty through the repurposing of available parts. Can recently acquired parts, previously foreign to an organism, be similarly repurposed? Applying a rigorous methodology to 319 genomes from arthropods, the largest phylum of animals, we uncover 104 novel genes that arose from the fusion of animal genes with fragments acquired via horizontal gene transfer from bacteria, viruses, fungi, and plants. RNA-Seq and RT-PCR across multiple species show that many of these novel genes are expressed as mRNAs. Many show signatures of evolutionary conservation and coherent domain architectures, suggesting that these chimeric genes may play important roles in diverse biological processes. These results reveal an understudied path to evolutionary innovation via "bricolage" of genes from across the tree of life.

evolutionary biology↗

bioRxiv2025

There and back again: the dynamic evolution of panarthropod germ cell specification mechanisms

Germ cells enable the reproduction of an organism and the continuity of its lineage. Across animals, these crucial cells are segregated from the soma at different times and places and via distinct mechanisms. Understanding the evolution of germ cell specification across animals is complicated by the difficulty of making meaningful comparisons of embryonic development between diverse animal species. Here, we characterize germ cell specification in Panarthropoda, an ancient clade that encompasses massive animal biodiversity, within which we can conduct meaningful comparative embryology. We amass data from centuries of studies describing the timing and mechanisms of germ cell formation, and apply ancestral state reconstruction to these data to propose novel hypotheses about the trajectory of evolution in this process. Furthermore, we speculate about the mechanisms underlying these evolutionary dynamics by considering the relationships among germ cell specification, concurrent developmental processes and the germ line gene network. Collectively, this Review derives new insights from a rich historical database of embryological observations, offering broad implications for understanding the evolution of metazoan germ cells.

evolutionary biology↗

bioRxiv2025

Protein sequence evolution underlies interspecies incompatibility of a cell fate determinant

Novel and rapidly evolving genes can integrate into conserved gene networks and play critical roles in development. Understanding how sequence variation across the orthologs of such genes influences functional interactions with the molecular products of older, more conserved genes requires investigation at the level of protein function. Here, we elucidate how protein-coding sequence evolution in oskar, a gene required for primordial germ cell specification and embryonic patterning in fruit flies, has led to functional incompatibility between orthologs from Drosophila melanogaster and Drosophila virilis. We generated chimeric versions of oskar comprising different combinations of Oskar protein domains from each species, expressed these chimeric oskar sequences in D. melanogaster, and quantified their ability to assemble functional germ line and abdominal patterning determinants (germ plasm). We found that a specific portion of D. virilis Oskar, namely the OSK domain, was primarily responsible for the cross-species incompatibility of Oskar. In the absence of endogenous D. melanogaster Oskar, chimeras containing the D. virilis OSK domain could not localize posterior germ plasm well enough to generate primordial germ cells, but were sufficient to specify the anteroposterior axis. We also found that the D. virilis OSK domain had dominant-negative effects on D. melanogaster Oskars ability to localize germ plasm mRNA, resulting in severe axial patterning defects. We propose that evolved changes in the biophysical properties of the OSK domain between species are linked to distinct molecular interactions with conserved germ plasm molecules. Under this hypothesis, an essential germ line determinant evolved to be incompatible across species of the same genus in less than 50 million years, while retaining functional within-species molecular interactions. This case study illustrates how investigating in vivo protein function can bridge genomic and molecular evolution with phenotypic variation and fitness at higher scales.

evolutionary biology↗

bioRxiv2025

The LOTUS domain of Oskar promotes localisation of both protein and mRNA components of Drosophila germ plasm

Germ cells transmit genetic information to the next generation in multicellular organisms. In Drosophila melanogaster, germ cells are determined by germ plasm, a specialised cytoplasm assembled by the Oskar protein. The current view of the molecular mechanism of germ plasm assembly attributes recruitment of protein and mRNA germ plasm components to distinct domains of the Oskar protein, called the LOTUS and OSK domains respectively. However, most evidence for this model is based on in vitro studies. Here we test the ability of Oskar variants to assemble functional germ plasm in vivo. We found that Vasa recruitment was largely unperturbed by LOTUS deletion or mutations in vivo. In contrast, nanos and pgc mRNA recruitment was affected by LOTUS domain perturbations, despite the current model attributing mRNA recruitment to the distinct OSK domain. Taken together, these data suggest a revision of the prevailing modular view of Oskars structure-function mechanism.

developmental biology↗

bioRxiv2025

Chinmo is a novel regulator of differential Hippo signaling response within a single developing organ.

Orchestrated control of proliferation of multiple cell types is essential for building a healthy organ. Here we use larval ovary development in Drosophila melanogaster as a model to understand the homeostasis of somatic and germ line cells in the formation of the female adult reproductive organ. We previously showed that the highly conserved Hippo signaling pathway regulates proliferation of both germ line and somatic cells in the D. melanogaster larval ovary. Response to Hippo signaling appeared to be mediated by different genetic mechanisms in germ line and soma, but the mechanism allowing distinct responses to the same signaling pathway remained unknown. Here we perform cell type-specific RNA-Seq of isolated germ line and somatic cells from the developing ovary at multiple time points spanning the formation of germ line stem cell niches, in either a Hippo signaling loss- or gain-of-function genetic background. Applying network analysis to these data revealed a novel regulator of ovarian development, the transcription factor chinmo. Subsequent experimental validation showed that chinmo acts as a key germ cell-specific translator of Hippo signaling in the developing ovary, allowing the Hippo signal to be transduced in cell type-specific ways in germ line and somatic cells within the same organ.

developmental biology↗

bioRxiv2025

Divergence of germ cell-less roles in germ line development across insect species

During development, sexually reproducing animals must specify and maintain the germ line, the lineage of cells that gives rise to the next generation of animals. In the fruit fly Drosophila melanogaster, germ cell-less (gcl) is required for the formation of primordial germ cells in the form of cells that cellularize at the posterior pole of the embryo, called pole cells. Forming pole cells is a mechanism of germ cell formation unique to a subset of insects. Even though most animals do not form pole cells as primordial germ cells, gcl is conserved across Metazoa, raising the question of how this conserved gene acquired its central role in the evolutionarily derived process of pole cell formation. Here, we examine the functions of gcl in two other insects with different modes of germ cell specification: the milkweed bug Oncopeltus fasciatus and the cricket Gryllus bimaculatus. We found that gcl is involved in germ cell development, but not strictly required for germ cell specification, in O. fasciatus, although it appears to function through a mechanism different from that in D. melanogaster. In contrast, we could not detect any impact on the embryonic germ line upon gcl knockdown in G. bimaculatus. This work serves as a case study into how the roles of genes in the process of germ line development can change over evolutionary time across animals. HighlightsO_LIgerm cell-less knockout reduces germ cell number in Oncopeltus fasciatus. C_LIO_LIgerm cell-less knockdown does not affect germ cell number in Gryllus bimaculatus. C_LIO_LIThe genetic mechanisms through which gcl affects germ cell number have diverged among insects. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=75 SRC="FIGDIR/small/645619v2_ufig1.gif" ALT="Figure 1"> View larger version (11K): org.highwire.dtl.DTLVardef@16ce97aorg.highwire.dtl.DTLVardef@1544b5eorg.highwire.dtl.DTLVardef@120219forg.highwire.dtl.DTLVardef@7f588e_HPS_FORMAT_FIGEXP M_FIG C_FIG

developmental biology↗

bioRxiv2024

Evidence for non-optimal codon choice in highly transcribed sex-biased genes of Drosophila melanogaster

Biases in synonymous codon use occur in many unicellular and multicellular organisms. Optimal codons, defined as those most commonly used in highly transcribed genes, are thought to arise from selection for cost-efficient translation, which would favor codons with abundant matching tRNAs. Such presumed selection is described as optimal codon choice. Non-optimal codons, defined as those least commonly used in highly transcribed genes, may in principle also play important roles, but the dynamics of their use remain understudied. Here we examine non-optimal codon use, using sex-biased genes expressed in the gonads of Drosophila melanogaster as a case study. We show that genes with sex-biased expression exhibit a preference for non-optimal codon use, especially testis-biased genes. Further we show that the use of non-optimal codons is not random. Instead, specific non-optimal codons are favored, again especially in testis-biased genes. Non-optimal codon use is positively linked to elevated disorder of the encoded proteins. Remarkably, all 18 degenerate amino acids were associated with higher disorder when encoded by the identified primary non-optimal codon, than when encoded by its sister optimal codon. We hypothesize that selection may have promoted non-optimal codon choice for a subset of favored non-optimal codons to regulate translation. We discuss the putative roles of tRNA gene copy numbers, pleiotropy, and sex-biased expression in the evolution of this level of gene regulation. Significance StatementOptimal codons, those codons most commonly used in highly expressed protein-coding genes, are thought to improve translational efficiency in a range of organisms. However, relatively minimal attention has been given to non-optimal codons, those least often used in highly transcribed genes, and their potential roles in translation. Here, using sex-biased gonadal genes of Drosophila melanogaster as a model system, we demonstrate that non-optimal codons are preferentially used in sex-biased genes, particularly within highly expressed testis-biased genes, and are associated with disordered proteins. Moreover, the preference for a specific non-optimal codon (per amino acid) is ubiquitous across all degenerate amino acids. We propose that non-optimal codon use is non-random and may have evolved under selection for roles in translational regulation and protein folding in sex-biased genes, and in a manner associated with their tRNA abundances. The findings have significant implications for the understanding of pacing of translation, protein conformation and protein functionality.

genetics↗

bioRxiv2024

Duplex PCR assay to determine sex and mating status of Ixodes scapularis (Acari: Ixodidae), vector of the Lyme disease pathogen

Ticks are a major health threat to humans and other animals, through direct damage, toxicoses, and transmission of pathogens. An estimated half a million people are treated annually in the United States of America for Lyme disease, a disease caused by the bite of a black-legged tick (Ixodes scapularis Say) infected with the bacterial pathogen Borrelia burgdorferi. This tick species also transmits another six human-disease causing pathogens, for which vaccines are currently unavailable. While I. scapularis are sexually dimorphic at the adult life stage, the DNA sequence differences between male and female I. scapularis that could be used as a sex-specific marker have not yet been established. We determine the sex-specific DNA sequences for I. scapularis (male heterogametic system with XY), using whole-genome resequencing and restriction site-associated DNA sequencing. Then we identify a male-specific marker that we use as the foundation of a molecular sex identification method (duplex PCR) to differentiate the sex of an I. scapularis tick. In addition, we provide evidence that this molecular sexing method can establish the mating status of adult females that have been mated and inseminated with male-determining sperm. Our molecular tool allows the characterization of mating and sex-specific biology across development for I. scapularis, a major pathogen vector, which is crucial for a better understanding of their biology and controlling tick populations.

genomics↗

bioRxiv2023

Gene protein sequence evolution can predict the rapid divergence of ovariole numbers in Drosophila

Ovaries play key roles in fitness and evolution: they are essential female reproductive structures that develop and house the eggs in sexually reproducing animals. In Drosophila, the mature ovary contains multiple tubular egg-producing structures known as ovarioles. Ovarioles arise from somatic cellular structures in the larval ovary called terminal filaments, formed by terminal filament cells and subsequently enclosed by sheath cells. As in many other insects, ovariole number per female varies extensively in Drosophila. At present however, there is a striking gap of information on genetic mechanisms and evolutionary forces that shape the well-documented rapid interspecies divergence of ovariole numbers. To address this gap, here we studied genes associated with D. melanogaster ovariole number or functions based on recent experimental and transcriptional datasets from larval ovaries, including terminal filaments and sheath cells, and assessed their rates and patterns of molecular evolution in five closely related species of the melanogaster subgroup that exhibit species-specific differences in ovariole numbers. From comprehensive analyses of protein sequence evolution (dN/dS), branch-site positive selection, expression specificity (tau) and phylogenetic regressions (PGLS), we report evidence of 42 genes that showed signs of playing roles in the genetic basis of interspecies evolutionary change of Drosophila ovariole number. These included the signalling genes upd2 and Ilp5 and extracellular matrix genes vkg and Col4a1, whose dN/dS predicted ovariole numbers among species. Together, we propose a model whereby a set of ovariole-involved gene proteins have an enhanced evolvability, including adaptive evolution, facilitating rapid shifts in ovariole number among Drosophila species. Significance StatementOvaries in Drosophila, like in other insects, contain egg producing structures, known as ovarioles. The number of ovarioles per female varies among Drosophila species, but little is known about the genes and evolutionary dynamics that may shape interspecies changes in ovariole numbers. Here, used a priori experimental and transcriptome data from D. melanogaster to identify genes involved in ovariole formation and functions, and studied their molecular evolution among its closely related species within the melanogaster subgroup. Using a multi-layered analysis consisting of protein sequence divergence (dN/dS), adaptive evolution, expression breadth, and phylogenetic regressions, we identified 42 genes whose molecular evolution patterns were well linked to ovariole numbers divergence. Further, gene protein sequence divergence was often predictive of species ovariole numbers.

evolutionary biology↗

bioRxiv2022

oskar acts with the transcription factor Creb to regulate long-term memory in crickets

Novel genes have the potential to drive the evolution of new biological mechanisms, or to integrate into pre-existing regulatory circuits and contribute to the regulation of older, conserved biological functions. One such gene, the novel insect-specific gene oskar, was first identified based on its role in establishing the Drosophila melanogaster germ line. We previously showed that this gene likely arose through an unusual domain transfer event involving bacterial endosymbionts, and played a somatic role before evolving its well-known germ line function. Here, we provide empirical support for this hypothesis in the form of evidence for a novel neural role for oskar. We show that oskar is expressed in the adult neural stem cells of a hemimetabolous insect, the cricket Gryllus bimaculatus. In these stem cells, called neuroblasts, oskar is required together with the ancient animal transcription factor Creb to regulate long-term (but not short-term) olfactory memory. We provide evidence that oskar positively regulates Creb, which plays a conserved role in long-term memory across animals, and that oskar in turn may be a direct target of Creb. Together with previous reports of a role for oskar in nervous system development and function in crickets and flies, our results are consistent with the hypothesis that oskars original somatic role may have been in the insect nervous system. Moreover, its co-localization and functional cooperation with the conserved pluripotency gene piwi in the nervous system may have facilitated oskars later co-option to the germ line in holometabolous insects.

animal behavior and cognition↗